This invention relates to a purified nucleic acid molecule, which is capable of expressing a lysosomal enzyme, wherein the nucleic acid molecule comprises at least a sequence coding for the lysosomal enzyme and a promoter highly active in the brain inserted upstream from the sequence.
Lysosomal storage diseases form a group of more than 30 metabolic disorders in which the function of one or several lysosomal hydrolases is deficient. Although the prevalence of each disease is low, prevalence of lysosomal storage diseases as a whole may be equivalent to that of cystic fibrosis in the general population (1:2500). In France, the most frequent lysosomal storage diseases are Gaucher type I disease, Hurler disease (MPS I), Hunter disease (MPS II), Sanfilippo disease (MPS III) and metachromatic leucodystrophy (MLD). They represent 10 to 50 births every year. With the exception of Gaucher type I disease, Pompe disease, Fabry disease and mild forms of MPS I, there is no etiological treatment available for lysosomal storage diseases so far. Bone marrow transplantation (BMT), which may be an option in some MPS I patients, is not effective in MPS III and MLD.
Lysosomal enzyme deficiencies induce the accumulation of intermediate catabolites in lysosomes, which progressively alters cell function and survival. Although deficiencies affect every tissue, clinical expression varies depending on the missing enzyme. Neurological symptoms are often predominant. They include severe motor impairments and mental retardation. Histopathology reveals characteristic vacuolizations in both neurons, glia and perivascular cells, without known predominance in specific locations. Other frequent symptoms include hepatomegaly, skeletal abnormalities, corneal clouding and respiratory, cardiac or renal dysfunctions leading to premature death. There is a need in the art for a treatment of the central nervous system pathology in lysosomal storage diseases in which neurological symptoms are either predominant, as in MPS III and MLD, or highly determinant for the clinical prognosis, as in MPS I. MPS I and MPS IIIb are autosomal recessive lysosomal storage diseases classified among mucopolysaccharidosis. These diseases are caused by a defect in the degradation pathway of glycosaminoglycans (GAGs). In MPS I and MPS IIIb, the degradation of heparan sulfates is interrupted by the deficiency of α-L-iduronidase (IDUA) and α-N-acetyl-glucosaminidase (NaGlu), respectively. Complete IDUA deficiency is associated with mutations W402X, Q70X and is responsible for severe forms of MPS I, in which skeletal abnormalities can be recognized at birth and neurological symptoms may occur before the age of 2–3 years. Milder forms exist in which the neurological disease is delayed and less severe (mild forms of MPS I or Hurler-Scheie disease) or even absent (Scheie disease). Except a frequent hepatomegaly, peripheral abnormalities are absent in MPS IIIb. Symptomatology appears in children between the age 2 and 6 as behavioral troubles, which progressively lead to a severe mental and motor degradation.
MLD is an autosomal recessive lysosomal storage disorder classified among the lipidoses. It is caused by a deficiency of arylsulphatase A (ASA) that leads to demyelination in the central and peripheral nervous system. Deficiency of ASA causes intralysosomal storage of the sphingolipid cerebroside sulphate. This lipid is abundant in myelin and its accumulation leads to the death of oligodendrocytes. ASA catalyses the first step in the degradation of the sphingolipid cerebrosisde 3-sulphate by removing the sulphate from the polar head of this lipid, which is a galactose 3-sulphate moiety. If this step does not occur, owing to a deficiency of ASA, this lipid cannot be degraded and accumulates into lysosomes. MLD may appear at any age. The three main clinical forms that correlate with the genotype can be distinguished: infantile, juvenile and adult forms. Allogenic BMT has no effect in the most frequent infantile form of MLD (>60% of the MLD cases) and limited effect in juvenile MLD.